Internal combustion engines, as are typically used in automotive and other engine-driven applications, are generally powered by the burning of a mixture of fuel and air in the combustion chambers of the cylinders in an engine. For many years, the carburetor was the preferred mechanism for controlling the mix of air and fuel. More recently, however, the carburetor has been largely superseded by the fuel injection system, since the fuel injection process usually provides better control of the parameters affecting engine performance.
Generally all new automobiles with internal combustion engines utilize some form of fuel injection system in an effort to enhance engine characteristics such as fuel efficiency, responsiveness and exhaust pollution control. While fuel injection systems vary widely, they are typically managed by an automatic electronic control system. For example, sensors are typically located in various parts of an automobile to provide feedback signals, such as engine speed, intake air temperature, driving conditions, and other parameters affecting engine performance. These signals are generally connected to a control processor within the electronic control system, which manages the operation of the fuel injection system in response to the sensor input signals.
A key element of a typical fuel injection system is the fuel injector, which usually includes a nozzle, a valve (e.g., a needle or ball valve) associated with the nozzle, and a compression spring. In a typical operation, the electronic control system causes fuel to be pumped into the injector with sufficient pressure to compress the spring. The spring forces the injector valve to open the nozzle, enabling a controlled burst of fuel mist to be sprayed into a corresponding combustion chamber. The fuel mist is combined in the chamber with a quantity of air appropriate for ignition.
The electronic control system generally provides for precisely timed opening and closing cycles of the injector valve, which can be in excess of 1,000 times per minute at highway speeds. In addition to controlling the timing of the injector open/close cycle, the electronic control system can also control the fuel supply, the ratio of air and fuel in the combustion chambers, and the timing of the ignition system. As such, a modern electronically controlled fuel injection system can provide a relatively high level of engine performance efficiency, with reduced exhaust emissions and improved fuel economy.
In order for an electronic control system to manage a fuel injection system efficiently, various strategies are employed for controlling the fuel-to-air ratio in the combustion chambers, as well as other factors. At least some of these control strategies are dependent on the temperature levels of various measured engine parameters, such as intake air, engine coolant, oil temperature and recirculated engine exhaust gas (EGR). However, cost and durability concerns limit the practicality of additional measurement devices in a mass-produced engine. Indirect estimating techniques are therefore often used to predict air intake or exhaust temperatures that are otherwise difficult to measure directly.
Another engine parameter that is difficult to measure directly is the operating temperature of a fuel injector tip, which will be referred to hereinafter as the fuel injector tip temperature, or FITT. Accurately predicting this temperature (FITT) under different engine operating conditions, such as running and restart, can enable an electronic control system to better correlate the injector temperature with a fuel compensation/enrichment strategy for optimizing engine performance.
In the case of a hot restart condition, for example, when a running engine has been shut down for a relatively short time (e.g., 15 to 45 minutes) and then restarted, it is possible for the fuel temperature to increase sufficiently to cause a vapor lock condition at the fuel injectors. That is, the fuel may vaporize because of its extreme temperature before it can be properly injected into the combustion chamber. When this occurs, it is generally desirable to implement some type of fuel compensation strategy, such as fuel enrichment (increasing the fuel-to-air ratio), or vapor purge, where the fuel tank vapor is captured and ingested into the intake manifold. It is therefore desirable to be able to predict the fuel temperature at the injector as accurately as possible under hot restart conditions, in order to provide an optimally efficient fuel compensation strategy.
Prior strategies for identifying hot engine restart conditions were typically based upon engine parameters such as shutdown time, shutdown coolant temperature, shutdown transmission oil temperature or shutdown air temperature. These parameters are generally cross-referenced to fuel compensation tables during the hot restart to determine the need for some type of fuel compensation strategy. This technique may falsely trigger excess fuel compensation and/or purge upon a hot restart, however, since the fuel compensation table information may not accurately represent the engine operating dynamics that cause hot fuel temperatures.
Accordingly, it is desirable to provide an apparatus and method for accurately predicting the FITT in an operating engine in which hot fuel temperatures exist. In addition, it is desirable to utilize the predicted FITT as a calibration basis for fuel compensation strategies. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.